When you will try to open CSV files in Calc it will show you a dialog, where you will be able to select/modify CSV import settings. The required settings to work with Magento CSV files are encoding (Unicode UTF-8), fields separator (comma) and text separator(double quotes).

Excel is a part of Microsoft Office software suite. You can find more information on it on the Microsoft Office Excel official homepage. Excel CSV-import and export setting depend on system wide regional options. In order to be able to work with CSV in Excel you have to modify them in the following way:

If you are a geek and you really know the CSV format specification, you may use any text editor that supports Unicode to edit CSV-files directly.

Listed hereafter some custom tools for editing CSV files:

A GOOD + FREE program
(actually a CardWare, meaning you have to send a postcard to the SW author)
is CSVed, capable of ‘massaging’ CSV files anyway you want.
There you find also uniCSVed with UniCode capabilites,
limited to Windows 2K & XP, only.
Also there: a brief but very interestingCSV introduction & tutorial

Feel free to add here any more CSV programs for authoring, editing, etc...